This week I discuss types of supernovae, specifically relating to the scenario where “Hydrogen lines are prominent in Type II supernovae but absent in Type Ia. Type Ia supernovae decline gradually for more than a year, whereas Type II supernovae alternate between periods of steep and gradual declines in brightness. Type II light curves therefore have a step-like appearance. Explain!”
Supernovae are classified as Type I or Type II depending upon the shape of their light curves and the nature of their spectra.
The question I really wanted to ask is ‘What happened to Type I or Ib?’ and the answer to that question was easily found in this chart:
Just in time for Halloween, my topic this week focuses on electron degeneracy pressure specifically to delve into how “A degenerate gas does not expand when the temperature increases as an ordinary gas does.”
In 1923, Arthur Stanley Eddington derived a formula to relate the luminosity of a star to its mass, and in the same year correctly interpreted high-density, white dwarf stars as being formed of matter so dense that atomic electrons have collapsed from their orbits, a substance we now call degenerate matter. (Levy, p. 116)
Young giant stars of a certain size, between .4 and 2 solar masses, have helium rich cores squeezed by gravitational force into a crystal-like solid. At these pressures, the atoms become completely ionized, separately into nuclei and electrons and are so closely crowded together that become influenced by the Pauli exclusion principle phenomenon. Two identical particles are not allowed to exist in the same place and time. As the electrons are pressed closer and closer together, the exclusion principle forces many of them to move faster and faster so they do not become ‘identical’ (meaning occupying the same space and moving with the same speed of adjacent electrons) and consequently this motion increases the repulsion between the electrons. This state provides pressure in the core preventing it from collapsing and is referred to by astronomers as degeneracy. Thus, low-mass giants with helium-rich cores are supported by electron degeneracy pressure. (Comins, p. 335)
Very high density matter, the structure of which is modified by the intense gravity. Particles, which must “squeeze”, create the degeneracy pressure.
This week I want to discuss “What might cause the closer of two identical stars to appear dimmer than the farther one?”
Apparent Magnitude: A measurement of the brightness of stars without regard to their distance from Earth.
The scale in use today starts with the star Vega and an apparent magnitude of 0.0
Objects brighter than Vega are assigned negative numbers. For example. Sirius, the night’s brightest star, has an apparent magnitude of -1.44
The scale was extended to include the dimmest stars visible through binoculars and telescopes. For example, a pair of binoculars can see stars with an apparent magnitude of +10
Ignoring distance for a moment, all other things being equal, the closer of two identical stars will appear brighter (have a smaller apparent magnitude) to us than the more distant star. When we account for the difference in distance, we use either or two measurements: absolute magnitude and luminosity.
I’ve reached the halfway point through my Introduction to Astronomy class. This week marks the eighth week of fifteen, sixteen if you count the first week where we just spent time getting to know each other and exploring the textbook and getting the lab software, Starry Night, installed and licensed. Last week, we reached the outer limits in the Kuiper Belt and Oort Cloud of our solar system where only comets and Voyagers I and II have ventured. Now we’ve snapped back to study our closest star, Sol, or more commonly just the Sun. My topic for discussion responds to the following question:
Why is the solar cycle said to have a period of 22 years, even though the sunspot cycle is only 11 years long?
Some surface features on our active Sun vary periodically in an eleven year cycle. The Sun’s magnetic fields which cause the surface changes vary over a twenty-two year cycle. The relatively cool and slightly darker regions, commonly called sunspots, are produced by local concentrations of the Sun’s magnetic field piercing the photosphere. The latitude and number of sunspots on average vary during the same eleven year cycle. But the hemisphere where the Sun’s north magnetic pole anchors during one eleven year cycle will have south magnetic poles during the next. Because it takes a full twenty-two years for the magnetic poles to return to their original orientation astronomers refer to the entire solar cycle. The magnetic dynamo model posits that many transient features of the solar cycle are caused by the effect of differential rotation and convection on the Sun’s magnetic field. The Sun’s differential rotation (different speeds at different latitudes) causes its magnetic field to become increasingly stretched like a rubber band. The bands can’t break so they periodically untangle themselves with the help of trapped gases which leak out (sunspot) and gradually settle back under the photosphere, when the sunspot disappears. The most recent reversal of the Sun’s magnetic field occurred in 2013. We are currently at the tale end of Solar Cycle 24. (Comins, 2015, p. 272-83)
My topic for discussion this week will attempt to answer the question:
Why do astronomers believe that the debris that creates many isolated meteors comes from asteroids, whereas the debris that creates meteor showers is related to comets?
But first, I want to share two things that serendipitously fell from my Twitter feed (@mossjon) today. Today’s APOD (Astronomy Picture of the Day@apod) featured the unusual mountain on Ceres (Comins, 2015, p. 239).
The second thing that immediately caught my eye today was an episode of Astronomy Magazine‘s “The Real Reality Show” entitled “How an Asteroid Killed Off the Dinosaurs” covered late in Chapter 8 of our textbook (Comins, 2015, p. 263-4) and which also bonked me on the head via my Twitter feed:
In this week’s discussion topic, I attempt to answer the question “Why are Uranus and Neptune distinctly bluer than Jupiter and Saturn?”
On Uranus and Neptune, the methane absorbs red, orange and yellow light, reflecting back the blue. In contrast, Jupiter and Saturn have only minor trace amounts of methane and quite a bit more hydrogen and ammonia.
This view of Uranus was recorded by Voyager 2 on Jan 25, 1986, as the spacecraft left the planet behind and set forth on the cruise to Neptune Even at this extreme angle, Uranus retains the pale blue-green color seen by ground-based astronomers and recorded by Voyager during its historic encounter. This color results from the presence of methane in Uranus’ atmosphere; the gas absorbs red wavelengths of light, leaving the predominant hue seen here. Image Credit: NASA/JPL
On the basis of lunar rocks brought back by the astronauts, explain why the maria are dark-colored, but the lunar highlands are light-colored?
Regions of both the near side and far side of the Moon not covered by mare basalt are called highlands. The highlands consist of the ancient lunar surface rock, anorthosite, and materials thrown out during the creation of the impact basins. (“Lunar Rocks | National Air and Space Museum,” n.d.)
The anorthosite rock highlands are brighter than the maria basalts. Pulverized by meteoric action, both the basalts of the maria and the anorthosite of the highlands are covered by a blanket of powdered rock, also known as regolith. Continue reading “Dark Seas and Bright Highlands”
Long answer: Still Jupiter, but let’s dive in and take a more detailed look.
Image Credit: NASA
Birth of a Gas Giant
A long time ago in a solar system very near you, just 1 or 2 AU past the snow line, enough surrounding planetesimals were accreted to become an Earth-like body containing about ten (10) Earth masses of metal and rock. This, in turn, gave this massive body enough gravitational attraction to pull vast amounts of hydrogen, helium and ices near its orbit, creating the first planet in our solar system: Jupiter. Impacts from the infalling gases and ices heated Jupiter up, so much so that for a short time, it outshown the protosun, if viewed from equal distances. Jupiter lacked the total mass to become a star, needing to be seventy-five (75) times more massive to achieve the necessary compression and heat in its core to sustain fusion.
This week’s discussion topic will attempt to answer the question:
Suppose your Newtonian reflector has a mirror with a diameter of 20 cm and a focal length of 2 m. What magnification do you get with eyepieces whose focal lengths are: a. 9 mm, b. 20 mm, and c. 55 mm?
From my textbook:
The magnification of a reflecting telescope is equal to the focal length of the primary mirror divided by the focal length of the eyepiece lens:
Magnification = Focal Length of Primary / Focal Length of Eyepiece
In the question stated above, the three different eyepieces will result in the following magnifications:
My second post in my series of weekly discussion topics for my Introduction to Astronomy online class. Last week I got up close and personal with the many sides of the Moon. This week I take a closer look at the other blue planet in our solar system and how we discovered it without observing it first.
The image is among the last full disk photos that Voyager 2 took before beginning its endless journey into interstellar space. (NASA Jan 1996)
Why was the discovery of Neptune a major confirmation of Newton’s universal law of gravitation?
Before Newton, astronomy relied on observational data from which mathematical formulae and equations were created. Newton pioneered an approach which allowed mathematicians to extrapolate and predict the movement of objects using three assumptions, now commonly known as his laws of motion. Together with his formula for gravitational force, Newton transformed Kepler’s three laws to predict orbits of comets and other solar system objects. He further formulated a mathematical model, known as the Law of Universal Gravitation, that describes the behavior of the gravitational force that keeps the planets in their orbits. (Comins, 2015, p. 42-44)
The anorthosite rock highlands are brighter than the maria basalts. Pulverized by meteoric action, both the basalts of the maria and the anorthosite of the highlands are covered by a blanket of powdered rock, also known as regolith. 
